As a conventional vibration power generation apparatus, an electrostatic induction vibration power generation apparatus is known in which an electric charge is applied to one electrode of a variable capacity and the electric charge is induced to another opposed electrode through electrostatic induction. The electric charge to be induced is varied by changing of the capacity. The electrostatic vibration power generation apparatus serves to generate power by taking out the change in electric charge as electric energy (see, for example, Patent Literature 1).
FIG. 16 shows a schematic cross-sectional view of a vibration power generator 10 disclosed in Patent Document 1 (see FIG. 4 and p. 10-11 of the same document), as one example of a conventional electrostatic induction vibration power generator using electret material.
The vibration power generator 10 includes a first substrate 11 with a plurality of conductive surface regions 13, and a second substrate 16 with a plurality of electret material regions 15. The first substrate 11 and the second substrate 16 are spaced apart from each other by a predetermined distance. The second substrate 16 including the electret material regions 15 is fixed. The first substrate 11 including the conductive surface regions 13 is coupled to a fixing structure 17 via springs 19. The spring 19 is connected to each side of the first substrate 11, and to the fixing structure 17. When the first substrate is displaced by an external force, the springs 19 can apply a restoring force to return the substrate to a certain position (to hold the substrate 11 in place). The presence of the spring 19 can cause the first substrate to reciprocate in the lateral direction (for example, in the horizontal direction in the drawing) and to return to the certain position.
The displacement of the first substrate 11 causes fluctuations in overlapped area between the electret material region 15 and the opposed conductive surface region 13, which results in a change in amount of charge on the conductive surface regions 13. The vibration power generator (electrostatic induction vibration power generator) 10 generates power by taking out the change in amount of charge as the electric energy.
A resonance frequency of vibration of the first substrate 11 is selected according to the frequency of the vibration to be used for power generation.